When drilling and/or routering a printed circuit board (PCT), a backup board is used to support the PCB either by applying it to the rear side of the PCB or by sandwiching the PCB with the backup boards. By using the backup board, a copper film of the PCB can be prevented from burring off during a drilling and/or routering process.
Conventionally, a backup board has been of a wooden board used for construction purpose, such as a particle board. However, a higher precision is required in processing the PCB these days and burrs on a copper film need to be reduced even more.
To lower the occurrence of burrs on a copper film, therefore, the backup board surface needs to be harder and smoother. A laminated resin plate made by processing a pile of prepregs of certain thickness under heat and pressure may serve this purpose due to its hard and smooth surface properties, a prepreg being made by impregnating paper with a thermosetting resin such as phenolic resin (see Japanese Patent Laid-open Application No. H08-118296).
However, the laminated resin plate has a poor workability due to its heavy weight with its specific gravity of about 1.4. Furthermore, due to the overall hardness of the laminated resin plate, the bits of a drill and/or router tend to be easily worn out. Another problem associated with using the laminated resin plate is that a paper-based resin plate may easily develop warps with a dimensional change caused by, e.g., moisture absorption. When the backup board develops warps in this manner, it may not support the PCB properly, thus failing to keep the level of burrs below an allowable limit.